It is desirable, particularly in clinical assay or analysis equipment, to have a diaphragm valve which can open without application of external forces, such as by vacuum assist. This is accomplished by pre-loading the diaphragm to an open position, then sealing the diaphragm with spring force on a plunger. However, manufacture of this type of valve is very difficult because of the tolerances which must be held to satisfy all field situations. For example, the valve may not open sufficiently quickly (within less than one second) because over a period of time there is a tendency for the polymer from which the diaphragm is formed to flow into a new configuration. With very tight tolerance specifications, new controlling software and careful assembly, this problem has been partially overcome, but the cold-flowing properties of the diaphragm material continue to present problems and has made production of a fully satisfactory product difficult. Although several types of diaphragm valves have been previously used, none of these valves can be used for a long period of time without the need for replacement.
One type of valve, known as the Porton valve, uses a pre-loaded formed or unformed diaphragm valve which moves away from the valve site when a plunger is retracted. Another construction known as the Grafunder design, involves movement of the diaphragm by vacuum away from the valve site when a plunger is retracted. Commercial products which use this technology are the Porton sequencer and Applied Biosystems analyzers.
The disadvantage of the Porton valve is its excessive cold-flow at the valve site if the valve is not used for long periods of time. The plunger retracts, but the diaphragm fails to open even though it is pre-loaded, because the pre-loaded force has been diminished by cold-flow. The disadvantage of the Grafunder design is the requirement for complicated subsystems to provide a vacuum above the diaphragm, including a vacuum source, a sealed plunger design, and generally more complexity in the valve arrangement. Additionally, if these diaphragms are made of an inert flexible material such as Kalrez, they will still cold-flow and fail to open. If Teflon is used for the valve, the Teflon will be very thin and will crack if moved often.
In order to overcome these problems, attempts had been made to glue the inert material to the end of a plunger. However, this approach was not successful in making a valve that seals completely and also withstands many actuations in the valve. Also, a number of other workers have attempted to provide diaphragm valves, but none of these has been entirely successful.
Thus, Rogers et al., in U.S. Pat. No. 2,324,880, discloses a valve diaphragm wherein the diaphragm is positively attached to a diaphragm actuator by a stud the head of which is embedded in the diaphragm body and surrounding the shank of a stud. An essential metallic ring prevents the elastic material between the shaft and the ring from stretching, thereby preventing the stud from being torn out of the diaphragm. The ring has a diameter roughly equal to that of the head of the stud. In this valve design, the ring is a critical element to prevent stretching of the diaphragm material, and the intent is to prevent the stud from being pulled away from the diaphragm. The valve disclosed is made of a material that can be rendered semi-plastic by the fluid which is being controlled by the valve.
Hughes, in U.S. Pat. No. 2,675,758, discloses a chemical feeder containing a diaphragm pump which provides pressure strokes by the uniform application of fluid under pressure over one face of the diaphragm. A machine screw is embedded in an enlarged central portion of the diaphragm and extends into a spring chamber. The diaphragm may be returned on suction strokes, upon release of the pressure, by its own resiliency or by means of a spring. When pumping under low head, the spring is not necessary, and the suction strokes can be accomplished solely by the resiliency of the diaphragm. There is no indication that the material of which the diaphragm is made can creep, only that the diaphragm is made of a flexible material such as neoprene.
McFarland, in U.S. Pat. No. 3,011,758, discloses valve diaphragms made of relatively stiff, inflexible material. All of the valves disclosed herein have various patterns of crests and hollows that act as bellows and provide gradual flexure which prevents localized and concentrated stresses which would develop cracks in the diaphragm.
Janquart, in U.S. Pat. No. 3,034,761, discloses an anti-caking dispenser valve. In this device, an annular, flexible diaphragm is in the form of a flange integrated with a shank to prevent incrustation around a movable armature. The diaphragm has a beaded portion at its outer periphery which is arranged to be received within an annular channel. A second laterally extending flange formed integrally with the shank and having a depending ring is arranged to seat against the lower surface of an outlet chamber, the depending ring arranged to provide a fluid tight seal at the outlet from the valve body. Two flanges are provided which are designed to break away incrustations of solidified fluid.
Saunders, in British Patent No. 434,665, discloses a diaphragm valve having flexible reinforcing means embedded in the diaphragm material to prevent the stud form being pulled through the disphragm material. The reinforcing material is used to prevent possible creep of the diaphragm material.
Fulton et al., in U.S. Pat. Nos. 4,734,190 and 4,810,392, disclose valves made of Kalrez. These valves are merely seals located at the end of a piston. The seals are of a dimension so as to rub against the piston cylinder and prevent intermixing of liquids.